Reading the Sectional, the Maximum Elevation Figure, and Picking Checkpoints You Can Actually Find on the Way to Oshkosh

The Maximum Elevation Figure (MEF) is the large blue number inside each grid square on a sectional chart, and it tells you the height above sea level of the tallest obstruction in that box. Read together with the VFR cruising altitude rule (FAR 91.159), it sets a safe floor for your cross-country and helps you choose a legal, terrain-clearing cruise altitude. Good cross-country planning pairs that altitude discipline with checkpoints you can actually identify from the air - distinctive, unique features spaced every 10 to 15 nautical miles along your route.

What Is the Maximum Elevation Figure on a Sectional?

The Maximum Elevation Figure, or MEF, lives inside every latitude/longitude quadrangle on your sectional - those boxes bounded by the thin blue lines. It represents the height, above sea level, of the highest obstruction inside that box. That obstruction might be terrain - a mountain or a ridge - or it might be a man-made obstacle like a broadcast tower.

The MEF is the single most important number for keeping you above everything in a given box. If you cross that quadrangle at or above the MEF, nothing inside it will hit you.

How Do You Read the MEF Number Correctly?

This is where many pilots - even licensed ones - get it wrong. The number looks like a fraction, but it is not one.

• The top number is thousands of feet.
• The bottom number is hundreds of feet.

So a 5 stacked over a 2 means 5,200 feet - not “five over two.” Misread it and you can talk yourself into an altitude that fails to clear the highest thing in that box.

There is also a built-in safety buffer. When chartmakers calculate the MEF, they take the highest known feature and add a margin. That margin accounts for survey tolerance in the feature’s exact height and for obstacles that may sit just below the charting threshold. The MEF is deliberately conservative by design.

How Do I Use the MEF to Pick a Cruising Altitude?

Before choosing a cruise altitude, run your finger down the entire route, box by box, and find the highest MEF anywhere near your line of flight. That value is your floor.

Whatever altitude you choose must sit comfortably above that floor - not resting right on top of it, but above it with room to breathe. Do this at the planning table before you ever fly.

What Is the VFR Cruising Altitude Rule (FAR 91.159)?

FAR 91.159, the VFR cruising altitude rule, works hand in hand with the MEF. It applies when you are in level cruise more than 3,000 feet above the surface, and your required altitude depends on your magnetic course:

• Easterly course (0° to 179°): fly odd thousands plus 500 - 3,500, 5,500, 7,500, and so on.
• Westerly course (180° to 359°): fly even thousands plus 500 - 4,500, 6,500, and so on.

Pilots call this the hemispheric rule, and its whole purpose is separation. Everyone going roughly your direction flies your kind of altitude, and everyone coming at you is 1,000 feet off. It is a simple, elegant way to keep airplanes from meeting in the middle.

How Do the MEF and Cruising Rule Work Together?

Here is how the chart and the regulation agree on a real trip.

Say you are flying into Oshkosh from the southwest on a magnetic course of about 040°. That is easterly, so FAR 91.159 gives you odd thousands plus 500: your candidates are 3,500, 5,500, and 7,500.

Now check the MEFs along your route. Suppose the highest is 2,800 feet. Technically, 3,500 clears it - but that leaves only 700 feet of margin over the worst obstacle, which is tight. 5,500 gives you real breathing room and still satisfies the rule. That becomes your altitude.

The chart set the floor, the regulation set the options, and you made a deliberate decision instead of picking a number that merely felt about right.

Wisconsin is not the Rockies - the terrain into Oshkosh is gentle. But building this habit on an easy trip is exactly the point. Let the MEF set your floor and the cruising rule set your options every time, so the discipline is automatic when you finally fly somewhere with real mountains.

Why Do Checkpoints Still Matter If I Have GPS?

Checkpoints are the features along your route that confirm you are where you think you are. Navigating by looking outside at the ground is called pilotage, and it still matters for two reasons.

First, the examiner expects it. The Airman Certification Standards (ACS) cross-country navigation task requires you to navigate by pilotage and dead reckoning. Second, the day your battery dies or your GPS drops out, checkpoints are what get you home. The magenta line is a wonderful helper and a terrible master.

How Do I Pick a Good Checkpoint?

A good checkpoint is something you can identify from several miles away, something unique, and something that lines up with your route. Break that down:

• Unique matters more than big. A single small town alone in farmland is a fantastic checkpoint - there is nothing nearby to confuse it with. One town in a cluster of five similar towns is useless. The same goes for roads: a lone highway crossing your course at an angle is excellent, but one road in a grid of identical section-line roads is worthless.
• Water is the champion. A distinctive lake, a bend in a river, or an oddly shaped reservoir stands out from 3,000 feet because water is dark, obvious, and unmistakable in shape. Wisconsin is covered in lakes, and heading into Oshkosh you have Lake Winnebago - a giant slab of water sitting right next to Wittman Regional Airport, arguably the best checkpoint in the whole state.
• Intersections of two linear features are next best. A highway crossing a railroad, or a river crossing a road, gives you a point rather than a line. A single line only tells you that you are somewhere along it; where two lines cross, that is a fix.
• Towers and antennas can work, but use caution. They are small and hard to spot until you are close - and by then they have stopped being a navigation aid and become an obstacle. That tall tower may be the very thing driving the MEF in its box. Everything on the chart connects.

How Far Apart Should Checkpoints Be?

Space your checkpoints about every 10 to 15 nautical miles in a typical training airplane. That is close enough that you are never flying long stretches wondering where you are, and far enough that you are not heads-down constantly.

Pick your checkpoints during planning, at the table, and write them on your navigation log with the time you expect to reach each one. In the air, all you are doing is confirming: airplane, meet lake, right on schedule. That is a calm cockpit and a pilot in command who knows exactly where they are.

How a Checkpoint Tells You What the Wind Is Doing

Picture a student pilot at about 40 hours, flying a longer cross-country toward the Oshkosh area during show week. The homework is done: a distinctive lake at the halfway point, a highway-railroad crossing three-quarters of the way, and Lake Winnebago as the terminal landmark. The highest MEF along the route is noted, and the cruise altitude clears it with margin while satisfying FAR 91.159.

Airborne, you reach the lake and your watch says you are two minutes early. That is valuable information: the wind is helping more than forecast, your groundspeed is up, and every remaining leg will arrive a little sooner. You adjust your time estimates - no panic, just a small correction based on a checkpoint doing its job.

A GPS groundspeed readout gives you the number. The checkpoint gives you the understanding, and understanding is what makes you the pilot the examiner wants to sign off.

How This Sets Up the AirVenture Arrival

As you approach the Oshkosh area during AirVenture, the airspace gets busy and the arrival procedure takes over. Everything above feeds directly into flying that arrival well.

You already know your altitude is right because you did the MEF and cruising-altitude work. You already know your position cold because you have been running checkpoints the whole way. So when it is time to descend, slow down, and find the railroad tracks and water tower everyone is looking for, you arrive relaxed and ahead of the airplane. The pilot who guessed for 200 miles arrives at Ripon frazzled; the pilot who planned arrives ready.

The regulations here come from the Federal Aviation Regulations and the FAA’s Airman Certification Standards, and the chart conventions are laid out in the FAA’s Aeronautical Chart User’s Guide - free, and worth every minute you spend with it.

Key Takeaways

• The MEF is the tallest obstruction in a sectional grid box; read it as thousands over hundreds (a 5 over a 2 is 5,200 feet), and it includes a built-in conservative safety margin.
• Find the highest MEF along your route first - that is your altitude floor - then use FAR 91.159 to pick a legal cruise altitude above it.
• Under FAR 91.159 above 3,000 feet AGL: easterly courses (0°–179°) fly odd + 500, westerly courses (180°–359°) fly even + 500.
• Pick checkpoints that are unique, identifiable from several miles out, and aligned with your route - water and crossing linear features are best.
• Space checkpoints every 10 to 15 nautical miles, log expected times, and use them to update your plan in real time.